Distraction osteogenesis is a technique which has been used to grow new bone in patients with a variety of defects. For example, limb lengthening is a technique in which the length of a bone (for example a femur or tibia) may be increased. By creating a corticotomy, or osteotomy, in the bone, which is a cut through the bone, the two resulting sections of bone may be moved apart at a particular rate, such as one (1.0) mm per day, allowing new bone to regenerate between the two sections as they move apart. This technique of limb lengthening is used in cases where one limb is longer than the other, such as in a patient whose prior bone break did not heal correctly, or in a patient whose growth plate was diseased or damaged prior to maturity. In some patients, stature lengthening is desired, and is achieved by lengthening both femurs and/or both tibia to increase the patient's height.
Bone transport is a similar procedure, in that it makes use of osteogenesis, but instead of increasing the distance between the ends of a bone, bone transport fills in missing bone in between. There are several reasons why significant amounts of bone may be missing. For example, a prior non-union of bone, such as that from a fracture, may have become infected, and the infected section may need to be removed. Segmental defects may be present, the defects often occurring from severe trauma when large portions of bone are severely damaged. Other types of bone infections or osteosarcoma may be other reasons for a large piece of bone that must be removed or is missing.
Intramedullary distraction devices and bone transport devices have been devised which can be adjusted non-invasively, using a variety of mechanisms such as magnets, motors, shape memory metals, and hydraulics. These devices are typically cylindrical and have a coaxially arranged, telescopic arrangement, in order to be low profile and allow for placement within the medullary canal of the bone. In these devices, the lengthening mechanism is typically assembled inside a housing, and then held in place by welds, for example, circumferential or axial welds. Welds may be created by laser, electron beam, or several other technologies. Depending on the design, the weld may need to withstand a large amount of stress, for a large number of cycles, and may also need to provide a hermetic seal when the device is implanted in the body of a subject. Typically, the strength of these devices is significantly below a typical solid or tubular trauma nail that is placed intramedullary in the canal of a broken bone. Because of this, patients with intramedullary distraction or bone transport devices must often use crutches and refrain from full walking for several months, in order to minimize the possibility of breakage of their implants.
In addition to intramedullary distraction and bone transport devices, other types of distraction devices are used in orthopedic applications. Examples include spinal distraction devices for treating scoliosis and other spinal deformities, mandible distraction devices for lengthening the jaw in patient with severe micrognathia and other extramedullary devices (attached to external portions of the bone to be lengthened or contoured). Because these devices are also subjected to high stresses and large numbers of cycles, the welds used to construct their housings are also challenged.
Non-invasively adjustable devices for spinal distraction are implanted in a surgical procedure, and then are non-invasively adjusted (e.g. lengthened) at regular intervals, such as monthly or quarterly. It is typical that an X-ray image is taken before and after the lengthening procedure, in order to visualize and confirm the amount of lengthening that has been achieved. If monthly lengthenings are performed, and if images are taken, both before and after the lengthening, then at least 24 x-ray images will be taken of that patient in one year. Some surgeons feel that only one image per lengthening procedure (for example, only after the lengthening) is needed, and others feel it might be done even less often. However, more information about the status of the lengthening of the implant is still desirable.